[PATCH v4 20/59] struct filename ->refcnt doesn't need to be atomic

Al Viro
2026-01-08T07:36:52Z

... or visible outside of audit, really. Note that references
held in delayed_filename always have refcount 1, and from the
moment of complete_getname() or equivalent point in getname...()
there won't be any references to struct filename instance left
in places visible to other threads.

Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 12 ++++++------
include/linux/fs.h | 8 +-------
kernel/auditsc.c | 6 +++---
3 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 4de9697bfbee..8f26e91de906 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -150,7 +150,7 @@ static inline void free_filename(struct filename *p)
static inline void initname(struct filename *name)
{
name->aname = NULL;
- atomic_set(&name->refcnt, 1);
+ name->refcnt = 1;
}

static int getname_long(struct filename *name, const char __user *filename)
@@ -292,13 +292,13 @@ void putname(struct filename *name)
if (IS_ERR_OR_NULL(name))
return;

- refcnt = atomic_read(&name->refcnt);
+ refcnt = name->refcnt;
if (unlikely(refcnt != 1)) {
if (WARN_ON_ONCE(!refcnt))
return;

- if (!atomic_dec_and_test(&name->refcnt))
- return;
+ name->refcnt--;
+ return;
}

if (unlikely(name->name != name->iname))
@@ -328,12 +328,12 @@ int delayed_getname_uflags(struct delayed_filename *v, const char __user *string

int putname_to_delayed(struct delayed_filename *v, struct filename *name)
{
- if (likely(atomic_read(&name->refcnt) == 1)) {
+ if (likely(name->refcnt == 1)) {
v->__incomplete_filename = name;
return 0;
}
+ name->refcnt--;
v->__incomplete_filename = do_getname_kernel(name->name, true);
- putname(name);
return PTR_ERR_OR_ZERO(v->__incomplete_filename);
}

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9fe91db9c053..6aaaf57e90d8 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2412,7 +2412,7 @@ struct audit_names;

struct __filename_head {
const char *name; /* pointer to actual string */
- atomic_t refcnt;
+ int refcnt;
struct audit_names *aname;
};
#define EMBEDDED_NAME_MAX 192 - sizeof(struct __filename_head)
@@ -2527,12 +2527,6 @@ void dismiss_delayed_filename(struct delayed_filename *);
int putname_to_delayed(struct delayed_filename *, struct filename *);
struct filename *complete_getname(struct delayed_filename *);

-static inline struct filename *refname(struct filename *name)
-{
- atomic_inc(&name->refcnt);
- return name;
-}
-
DEFINE_CLASS(filename, struct filename *, putname(_T), getname(p), const char __user *p)
EXTEND_CLASS(filename, _kernel, getname_kernel(p), const char *p)
EXTEND_CLASS(filename, _flags, getname_flags(p, f), const char __user *p, unsigned int f)
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 67d8da927381..86a44b162a87 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -2191,7 +2191,7 @@ void __audit_getname(struct filename *name)
n->name = name;
n->name_len = AUDIT_NAME_FULL;
name->aname = n;
- refname(name);
+ name->refcnt++;
}

static inline int audit_copy_fcaps(struct audit_names *name,
@@ -2323,7 +2323,7 @@ void __audit_inode(struct filename *name, const struct dentry *dentry,
return;
if (name) {
n->name = name;
- refname(name);
+ name->refcnt++;
}

out:
@@ -2445,7 +2445,7 @@ void __audit_inode_child(struct inode *parent,
if (found_parent) {
found_child->name = found_parent->name;
found_child->name_len = AUDIT_NAME_FULL;
- refname(found_child->name);
+ found_child->name->refcnt++;
}
}

--
2.47.3